Best way to choose a random file from a directory in a shell script

Question

What is the best way to choose a random file from a directory in a shell script?

Here is my solution in Bash but I would be very interested for a more portable (non-

Answer 1

I think Awk is a good tool to get a random number. According to the Advanced Bash Guide, Awk is a good random number replacement for $RANDOM.

Here's a version of your script that avoids Bash-isms and GNU tools.

#! /bin/sh

dir='some/directory'
n_files=`/bin/ls -1 "$dir" | wc -l | cut -f1`
rand_num=`awk "BEGIN{srand();print int($n_files * rand()) + 1;}"`
file=`/bin/ls -1 "$dir" | sed -ne "${rand_num}p"`
path=`cd $dir && echo "$PWD/$file"` # Converts to full path.  
echo "The randomly-selected file is: $path"

It inherits the problems other answers have mentioned should files contain newlines.